MAST - Mega Ampere Spherical Tokamak

The MAST experiment has been in operation at Culham since December 1999. It follows the highly successful START experiment (1991 - 1998), to further explore the spherical tokamak (ST) approach. MAST uses the same innovative spherical tokamak design as START, which has shown itself to be more efficient than the conventional toroidal design, adopted by JET and ITER. START proved to exceed even the most optimistic predictions and the purpose of MAST is to confirm the results of its forerunner by using a larger more purpose-built experiment.

Spherical tokamaks differ from conventional JET-ITER style tokamaks in the shape in which plasma is held by magnetic fields. The more compact spherical shape (as opposed to conventional doughnut shape) may have potential as a more efficient and economical fusion power plant design, as well as providing direct input into the ITER databases.

MAST research is funded jointly by the Engineering and Physical Sciences Research Council and Euratom.

Main Objectives

The main objectives of MAST are:

  • Studies in a new regime, to provide improved understanding of tokamaks, and improved ITER design (e.g. effects of plasma shaping).
  • To investigate the potential of the spherical tokamak route to fusion power.

Plasma Heating on MAST

Plasma heating and current drive on MAST uses Neutral Beam Injection (NBI) and Electron Cyclotron Resonance Heating (ECRH).

Two NBI beamlines on loan from Oak Ridge National Laboratory will inject powers up to 2.5 MW per injector for pulse lengths up to 0.5 s, and 2 MW for pulse lengths between 0.5 s and 5 s, and are predicted to drive approximately 0.5 MA of current at a density of 2 x 1019 m-3. These injectors use diopigratron ion sources coupled to triode accelerators, both of which are being upgraded to operate at beam energies up to 70 keV and pulse lengths up to 5 s. To date, one injector is operational at the 1 MW level; the second is being commissioned.

Options for RF plasma heating on MAST are limited by the combination of high density and low magnetic field. An ECRH system comprising seven 60 GHz gyrotron sources has been used to couple 0.6 MW to the plasma to date, with the final objective of 1 MW coupled power. Bernstein wave heating is being investigated; this will overcome the density limitation.

More information on MAST can be found on the UKAEA Fusion web site.